Threaded fasteners and threaded fastener systems including male and female members are used extensively in a variety of assemblies and constructions. It is known to use a male threaded member in combination with a female threaded member comprising a stamping or other plate-like or cupped member, in which a single helix thread is provided in the female member. A problem with threaded fastener systems having female members with a single helix thread is that the fastener can become loose due to vibration and other external forces exerted against the fastening system. The small amount of surface contact between the male fastener component and the single helix thread of a stamped female member is one cause for this undesirable effect. When the male and female member start to move, the natural ramped surface contact between the surfaces allows the system to loosen. While the significance of this problem can be reduced to some extent by providing additional thread length in the female member through the inclusion of additional helixes in the thread, in some assemblies and constructions there is insufficient room for providing additional length to the female member. Further, the member becomes more complex and difficult to manufacture, thereby increasing the cost of the fastening system, as the simple stamping procedures used for a single helix fastener system may not be satisfactory for a more complex fastener system.
Is it also known to provide fastening systems in which the female member is clipped or in some way connected to an object such as a piece of sheet metal or other thin material. Although in some fastening systems the female members have considerable thickness, thereby providing a thread including several helix wraps, loosening of the fastener system continues to be a problem. If the material to which the female member is connected is relatively thin with minimal strength, such as thin-gauge sheet metal, the material can bend or deflect as additional torque is applied to the male member, to bind the threads of the male and female member more tightly. Thus, since only minimal torque can be applied, the fastener system can be loosened easily through vibration and other external forces.
Another problem sometimes experienced is strip-out due to over-tightening of the fastener. Particularly in assemblies that are lightweight, in which the fasteners also are lightweight, it may be difficult to determine when sufficient torque has been applied for optimum fastener performance. Under tightening can lead to loosening in use, and over tightening can result in strip-out. The acceptable torque window available for proper tightening may be quite small.
Male threaded members anchored in plastic have similar and additional problems. It is desirable to provide a screw that drives in easily, straight and that fastens securely. Modifying thread profiles to improve resistance to pull-out has resulted in blunting the thread crest, which can cause excessive material removal as the screw is driven. Material removal reduces the holding strength of the fastener.
What is needed in the art is a male threaded member and a threaded fastening system that improve retention between the male threaded member and the female threaded member or anchoring material in which the fastener is secured for a variety of applications, including threaded fastening systems having female members comprising a single helix thread, and fastening systems applied to relatively thin material limiting the torque that can be applied in making the threaded connection. What is further needed is a male fastening member that drives easily and straight, with increased holding strength in plastics and other similar materials.